1. Field of the Invention
The present invention relates to a fluid control system, and in particular to a fluid flow control valve. In one application, the fluid flow control valve can check the free flow of water from a broken or damaged riser of an overhead irrigation system.
2. Description of Related Art
Overhead irrigation systems often incorporate water spray devices (e.g., sprinkler heads) mounted on risers. Risers can either be fixed or movable, e.g., pop-up type sprinklers. A riser supports a sprinkler some distance above the ground, e.g., a few inches to several feet high. At this elevated position, the sprinkler has an enlarged spray pattern and irrigates a larger area than if the sprinkler were positioned closer to the ground. Riser mounted sprinklers also accommodate crops of varying heights.
Risers are pipes or conduits, typically made of plastic such as polyvinylchloride ("PVC"), copper, brass, or galvanized steel. In many irrigation systems, the riser extends upward from a fitting of the irrigation system, such as from a "T" or an elbow juncture, located under ground. In such an arrangement, water flows from a subterranean irrigation pipe through the riser to the sprinkler. In a pop-up type sprinkler, a movable riser extends from a housing when the sprinkler is in use. This enables a sprinkler head attached to an end of the riser to rise to a predetermined height to deliver fluid to the surrounding area.
While the use of a riser-mounted sprinkler head enlarges the area irrigated by the sprinkler, the riser is susceptible to mechanical damage because it extends above ground in an exposed position. Because typically no external structure braces or buttresses the riser, the riser can be broken (e.g., severed) or otherwise damaged (e.g., theft, vandalism, etc.), resulting most often in an open, free-flowing outlet. In addition, if the sprinkler head is removed from the riser, fluid will flow freely from the riser.
When a riser is broken or the sprinkler head is removed, water cannot be properly distributed through the sprinkler head. The rate of water flow increases without the restricting back pressure provided by the sprinkler, such that a large stream of water projects above the broken riser. The resulting water geyser impacts against a relatively small ground surface. Serious flooding and erosion consequently results in a small area, while the remainder of the area normally irrigated by the sprinkler goes unwatered. A significant amount of water is wasted as the result of the unrestricted flow through the broken riser, and substantial soil erosion can occur.
In addition, the water fountain gushing from the broken riser also can pose a serious highway problem if the water sprays onto highway lanes, or if the resulting water and soil run-off flows onto the highway. Numerous automobile accidents occur each year due to broken irrigation system risers.
While valves exist in the prior art for control of fluid flow in general, many such valves are inappropriate for restricting the flow of irrigation water through a riser with a free-flowing outlet, e.g. a broken or damaged riser, or a riser without a sprinkler head. Additionally, high volume farm irrigation systems introduce special needs for flow control. Prior valves are overly complicated and expensive for application to farm irrigation systems, which utilize hundreds of riser-mounted sprinklers. Some devices which have been implemented for stanching the unrestricted flow of irrigation water have proven unreliable, often failing to stop or even slow the rate of water flow when a riser breaks or other failure occurs. Other prior devices are too sensitive, shutting down water flow to undamaged risers.
In addition, when prior devices do function to stop the flow of water through a broken riser, the broken sprinkler often remains undetected for days, leaving the area surrounding the broken sprinkler unwatered. This danger is especially true of farm irrigation, where a single broken riser in a large field with many sprinklers could easily escape notice for many days, damaging crops in the vicinity.
Further deficiencies in prior devices include an inability of these devices to cope with transient flow conditions. For instance, the prior devices may prematurely shut off the valve in response to the combination of air and water in the system that often occurs when the system is first turned on. In addition, prior devices often include improperly restrained components which vibrate and wear under normal flow conditions.
Prior devices also have close fitting parts which are subject to corrosion. As a result, the small space between the parts cannot be maintained as corrosion, scale, debris, etc., often fill the space between the closely fit parts, and the device is likely to malfunction. For example, in a prior valve, a disc or poppet is shaped and sized to have a close fit with the valve seat in order to arrest fluid flow under abnormal flow conditions. Upon corrosion, however, the disc or poppet will not properly seal the valve seat, thereby allowing fluid flow within the valve. Under some conditions, such corrosion, scale formation, or like collected debris will prevent the valve disc or poppet from moving at all.
A need therefore exists for a simple, inexpensive yet reliable irrigation control valve which allows water to flow to an operational sprinkler, but restricts the water flow through a free-flowing outlet of the riser. Ideally, such a valve should allow detection of the broken riser or missing sprinkler head, even when the flow through the riser is essentially shut off